1. Technical Field
The embodiments herein generally relate to wireless communication systems, and, more particularly to Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) and Integrated Services Digital Broadcasting-Terrestrial Sound Broadcasting (ISDB-TSB) systems.
2. Description of the Related Art
In recent years, the wireless industry has seen explosive growth in device capability, especially in relation to mobile devices, such as cell phones, handhelds, gaming consoles, etc. Ever-increasing demand for computing power, memory, and high-end graphic functionalities has accelerated the development of new and exciting wireless services. In the last few years, multiple technologies have been proposed to address the delivery of streaming multimedia to mobile devices.
Multimedia communications provide a rich and immediate environment of image, graphics, sound, text, and interaction through a range of technologies. An example of multimedia communication is streaming multimedia, which is primarily a delivery of continuous synchronized media data. The streaming multimedia is constantly received by, and displayed to, an end user while it is being delivered by a service provider. Multiple technologies such as ISDB-T, Integrated Services Digital Broadcasting-Terrestrial Sound Broadcasting (ISDB-TSB), Terrestrial-Digital Multimedia Broadcasting (T-DMB), Satellite-Digital Multimedia Broadcasting (S-DMB), are used to address the delivery of streaming multimedia to mobile devices. These technologies have typically leveraged upon either third generation cellular/PCS or digital terrestrial TV broadcast technologies.
ISDB, as the name suggests, is used for digital transmission and reception of integrated services, such as television, audio and data services. ISDB includes a variety of transmission standards for broadcasting of satellite, terrestrial, and cable signals. The ISDB transmission system utilized for broadcasting terrestrial digital television signals is termed as ISDB-T and ISDB-TSB.
The ISDB-T and ISDB-TSB systems are based on Orthogonal Frequency Division Multiplexing (OFDM). A number of OFDM segments may constitute a plurality of transmission bands in the ISDB-T and ISDB-TSB transmission systems. The ISDB-T system is enabled to individually set operating parameters of each OFDM segment, thereby enabling a formation of flexible channels. Furthermore, signals in the ISDB-T system are transmitted in the form of symbols having different number of bits based upon the modulation system being used. An OFDM frame consists of 204 symbols having a sufficient guard interval in between to prevent inter-symbol interference effects. Moreover, the ISDB-T system utilizes Moving Pictures Expert Group-2 (MPEG-2) video coding and MPEG-2 Advanced Audio Coding (AAC), thereby enabling a simultaneous transmission of audio, video, and data. The audio, video, and data may be multiplexed to form a single transport scheme for transmission to the receiver. Additionally, a Transmission Multiplexing Configuration Control (TMCC) signal is transmitted with the multiplexed data to other information such as channel segment configuration and transmission parameters.
ISDB-T provides elements in operation and reception that are common to those in digital satellite broadcasting and communications. It also provides flexible multi-program editing for different reception conditions by hierarchical transmission in a transmission channel. The transmission parameters for each hierarchical layer can be selected independently of each other. A transport stream (TS) is re-multiplexed and arranged into data groups (data segments) prior to OFDM framing. In ISDB-T, the transmission parameters of the modulation scheme of OFDM carriers, the coding rates of inner code, and the length of the time interleaving can be independently chosen for each data segment. Hierarchical transmission of ISDB-T is achieved by transmitting OFDM segment groups having different transmission parameters in a channel. A maximum of three layers (three different segment-groups) can be transmitted in one channel at the same time.
Conventionally, the ISDB-T system features three transmission modes, referred to as Mode 1, Mode 2, and Mode 3. Each OFDM segment of the three modes has different number of carriers, thereby enabling the use of wide range of transmitting frequencies for the system. Additionally, the ISDB-T system may be utilized to provide high quality and reliable video, audio, and data broadcasting for fixed as well as mobile receivers.
In a typical environment, frame synchronization is based on the frame boundary, and the receiver does not start data processing and decoding until the frame boundary is detected and synchronized. One of the major problems with this synchronization scheme is long latency. In the worst case, it introduces a latency of almost one frame. One can tell the frame boundary by the OFDM symbol number. In ISDB-T and ISDB-TSB, the symbol number counts from 0, 1, . . . , to 203, and after it reaches 203, it resets and counts from 0, 1, . . . , to 203 again. Symbol number 0 indicates a start of a frame. The receiver monitors the symbol number and when it detects the current symbol number is 0, it starts to perform data processing and decoding. The drawback of this scheme is long latency and long synchronizations. For an end-user, it means more waiting time for video and audio whenever he switches to a new audio/video channel.